Bennett Science Blog

Photo Credit: Damia Bouic, DARTS, ISAS, JAXA By Amber Bennett You'd think that the rotational speed of a planet would remain constant. Take earth for instance. At the equator, the planet spins at roughly 1,600 km/hr (1,000 mph), and that speed doesn't change much, which gives us our consistent 24-hour days. However, scientists have discovered that Venus doesn't have a constant rotational speed. In fact, it can speed by up to 2 minutes per Venus day. The reason? The extremely thick atmosphere that surrounds the planet, which moves faster than the planet spins. With the help of computer models, researchers found that the winds on Venus move an astonishingly 100 m/s (about 224 mph)! That's about a third of the speed of sound on earth. Measurements of Venus' day length, or rotational period, can vary by up to 7 minutes, likely because of how the atmosphere moves against the mountains. It's important to note that the rotational speed isn't constantly...

YouTube Screenshot (https://www.youtube.com/watch?v=eu_WRsxGnK0) By Andrew Bennett What Is the Law of Reflection? If you have ever played pool, you've probably done a little mental geometry that looks very similar to the Law of Reflection. This law simply states that whenever a wave hits a boundary and reflects, the angle it reflects at is equal to the angle at which it hit the boundary. Lining up a bounce shot in billiards requires the same thinking. What Is Specular Reflection?  Very flat surfaces (such as calm water, glass, and mirrors) make such clear reflections because every bit of light that hits the surface will encounter a surface at exactly the same angle. In physics, we describe this as regular or specular reflection. Specular reflection. YouTube Screenshot (https://www.youtube.com/watch?v=eu_WRsxGnK0) What Is Diffuse Reflection? Surfaces that aren't as polished (such as walls, clothes, or skin) have tiny bumps covering them.  When light h...

YouTube Screenshot (https://www.youtube.com/watch?v=E1lCjq4IzJw) By Andrew Bennett Cavendish Experiment Build Update At this point, the device itself is built except for plastic sheeting covering the whole thing. The next step is to set up the lasers and mirrors for making extremely precise measurements of angles. Cavendish Gravity Experiment FAQs I've received a lot of feedback and questions on my previous Cavendish videos . Here's a look at the frequently asked questions. "Doesn't his need to be done in a vacuum to eliminate air currents as a variable?"  This will not be conducted in a vacuum. As far as I can tell, that would make this nearly impossible.  Removing the air from the container requires a significant amount of air movement, which would get the torsional balance swinging. Since air resistance is really the only force slowing down that swinging, you'd be stuck with way too much movement to make a good measurement. I also don't...

YouTube Screenshot (https://www.youtube.com/watch?v=X3hp5p8RDNw) By Andrew Bennett Fence posts are often set in concrete to keep them stable, which is great ... until you have to remove them. I've seen people dig all around the concrete to free the post, but that is way more digging than I want to do. Instead, you can make a long lever to remove it without any digging at all! What Is a Lever? A lever is just a stiff arm that can pivot around some point (the fulcrum) so you can apply a force to one part of the arm and get out a force from another part of the arm. This can be used to change the magnitude or the direction of a force, making a small force large or an upward force downward. This mechanism hinges on (sorry, couldn't resist) the idea of rotational equilibrium . As long as the arm is at rest or moving at a consistent speed, the total torque on the arm must be zero because its angular acceleration is zero. When you use a lever to lift something, these conditio...

Photo Credit: Zátonyi Sándor/Wikimedia Commons By Andrew Bennett In this blog post, you will learn how to model an object's position as it undergoes simple harmonic motion using sine or cosine functions. Simple Harmonic Motion Refresher Simple harmonic motion is defined as periodic motion caused by a restoring force that is proportional to the object's displacement from equilibrium. This definition might seem arbitrarily complicated, but there are good reasons for separating this type of motion. For this post, it is important to note that the position, velocity, and acceleration of any object undergoing simple harmonic motion can be described using the sine and cosine functions. We might not be able to model other types of repeated motions with simple equations like this. Sine Function for SHM A general form frequently used here for the sine function is: x ( t ) = A *sin (ꞷ t ) Where: x = the position at some moment in time A = the amplitude of the motion...

YouTube Screenshot (https://www.youtube.com/watch?v=l-VRjwe_EHU) By Andrew Bennett What Is the Torsion Constant? The Cavendish gravity experiment involves a balancing of torques on the torsion balance . On the one hand, we have gravity from heavy objects placed near the ends of the balance trying to twist the whole thing in one direction. Opposing that, we have the wire trying to untwist. That "untwisting ability" is described by a number called the torsion constant of the wire . If we are to get a measurable deflection from the Cavendish experiment, we need to use a material for the wire with a very low torsion constant. Testing the Constant Using a Torsional Pendulum Testing for the torsion constant directly requires special equipment to measure very small torques. In this video, I test it indirectly by setting up a torsional pendulum (so that the bar on the wire twists back and forth repeatedly). I do this because the relationship between the period of a torsiona...

YouTube Screenshot (https://youtu.be/qqyxKSsXX7A) By Andrew Bennett In order to replicate the Cavendish gravity experiment and experimentally determine a value for the universal gravitation constant, I built a torsion balance. This revised design is longer than anything I've used before. It also gives me the flexibility to adjust the positions of the attachment points for the wire and the weights. What Materials Are Included? PVC pipe is used as the base for the brackets. I heated it with a heat gun, then molded it to the aluminum bar. The weights are currently dumbbell weights with a bottle cap turned into an adapter between the dumbbell mounting holes and the small bolts. If viewing via email, click here to see the video. What's Next in the Cavendish Gravity Demo Series? In the next video, I'll be using the torsion balance as a torsion pendulum to evaluate the torsion constant of the different string and wire options for the Cavendish experiment.  Please b...